2.4.2. Colorimetric determination of total phenols
Total phenols were determined by using the Folin–Ciocalteu reagent
as reported by Gutfinger (1981). A 0.5 ml aliquot of olive methanolic extract
was introduced into a test tube and mixed with 1 ml of 0.5 M
Folin–Ciocalteu reagent. The mixture was allowed to stand for 5 min,
then 3 ml of 200 g/l sodium carbonate solution was added and the volume
was made up to 10 ml with distilled water. The solution was stirred
and allowed to stand for 30 min at roomtemperature. The mixture was
then centrifuged for 10 min at 6000 ×g and the absorbance of the supernatant
was measured at 725 nm on a spectrophotometer (Lambda 25
UV/Vis Spectrophotometer, PerkinElmer, USA). Total phenolics were
expressed as mg caffeic acid per 100 g of pulp dry weight.